Activity 14C: T-Charts, Decay Curves, and Half-Lives

  • Due Jan 31, 2021 by 11:59pm
  • Points 15
  • Submitting a file upload
  • Available after Jan 25, 2021 at 12am

T-Charts, Decay Curves, and Half-Lives

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Helpful tips to calculate a half-life:

  • Draw or insert a T-chart.
  • In the T-chart, label the left side with time units (number of half-lives, years, ka, Ma, Ga, etc.)
  • Label right side with mass units (percentage, atoms, gram, kilograms, etc.)
  • Begin by ALWAYS writing zero in the first spot of the time column.
  • In the mass column, begin with the given mass if provided. Recall that this is 100% of the original parent isotope.
    • If the mass is the starting mass, keep dividing the number in the mass column by 2 for each half-life in the left column.
    • If you are given a final mass, record this at the very bottom of the mass column.
      • If the mass given is the final mass, multiply that mass by 2 until the initial time (Time 0) is reached.
      • The final mass amount at the bottom of the mass column equals how much mass is left after radioactive decay has occurred.
    • In the time column, add one half-life at a time until you reach the total time given in problem. The number of half-lives elapsed is equal to the number of times you added a half-life in the time column.

1. Calculate the amount of parent isotope remaining for all the given half-lives in this T-chart.

Table 14.4: T-chart to use in question 1-3 in Activity 14C: T-Charts, Decay Curves and Half-lives. (CC-BY 4.0, Chloe Branciforte)
Number of Half-lives Amount of Parent Isotope Remaining (%)
0 100

2. Plot your findings from the T-chart on the graph below.

3. Draw the decay curve by connecting your plotted data points.

Graph to use for plotting T-Chart data and to draw in the decay curve.

Figure 14.23: Graph to plot data and draw decay curve for Activity 14C: T-Charts, Decay Curves and Half-lives.(CC-BY 4.0, Chloe Branciforte, own work)

Using the above graph (Figure 14.25), answer the following questions.

4. How much of the parent isotope would be remaining after 7 half-lives have passed?

    • 6.25%
    • 1.56%
    • 0.78%
    • 0.39%

5. If a radiometric element has a half-life of 425 years, how old would a rock be that only had 3.125% of the parent isotope remaining?

    • 2125 years
    • 1700 years
    • 2550 years      
    • 3400 years

6. Approximately how much of the parent isotope would be remaining after 3.5 half-lives?

    • 16%
    • 12%
    • 4%
    • 8%

7. Based on your graph above, approximately how many half-lives have passed when only 35% of the parent isotope is remaining?

    • 0.75
    • 1.5
    • 2.1
    • 2.5
1612166399 01/31/2021 11:59pm